Tube Preamp Turn-on Transients

cbl117

I have a technical question for you guys, but first some background. I use a tube preamp with a solid state amp. I always turn on my components in the same sequence which is source-preamp-amp. But I have noticed that if I turn on my amp before the tube preamp is done doing its warm up, as soon as the preamp goes into normal operation mode, it switches my parasound amp into protection mode for a few seconds. My questions are as follows. Is this caused by normal turn on transients from my preamp? Is there something wrong with my preamp or could I be damaging my amp?

fredv

Most if not all tube preamps have a output capacitor. When the pre is power up, this will be charged out in the first few seconds. During this "charge up" period, the cap will experience some kind of disturbance that has very low frequency. The frequency is so low that some amps will see it as DC and hence run into protection mode. In some cases, the amp doesn't run into the protection mode, instead it passes the low freq to the speakers. Some speaker's driver can be blown by this LF!!! This scenarios usually happens to the SS amp because tube amp simply won't have this low frequency response. Most modern tube pre's have a relay that short the output for a few seconds to a couple mins to avoid such unpleasant instance.

In short, your amp did the right thing, and there is nothing wrong with the pre tube. Just make sure they are powered on in the right ordering.

cbl117

Thanks fred. I thought thats what it was but just wanted some more opinions.